Positioning devices of this type are often used in servo track writers (STW), where the tracks are arranged or written for magnetizable hard disks. For this purpose, a positioning device in the STW swivels a shaft, to which a swivel arm is attached. At its end, a write head is provided which is ultimately moved by the swivel motion of the shaft and is positioned in a highly precise manner, so that as many tracks as possible can be configured per unit surface area of the hard disk. The number of tracks arranged per unit surface area or unit diameter (tracks per inch) is a measure for the storage capacity of hard disks. For this reason, efforts are continuously made to achieve a track format that is as tight as possible. To permit a hard disk manufacturer to configure hard disks with a tight track format in an economical manner, it must be possible to exactly position the swivel arm of the STW within a very short time (seek and settle time).
German Published Patent Application No. 103 57 295 describes a positioning device, which has two bearing units, each made up of two ball bearings, for supporting a shaft. To support the shaft in a statically defined manner, bearings are disposed so that they are axially displaceable in the housing of the positioning device by corresponding fits. For conventional positioning devices, there is the danger that such floating bearings will not be torsionally stiff, e.g., that in response to high angular accelerations, tangential relative movements can occur between the shaft and/or the housing and the bearing.